In recent years, along with the enhancement of operation speed of personal computers, the spread of network infrastructure, and an increase in capacity and a decrease in price of data storage, the opportunities of obtaining pieces of information such as documents and images, which have been provided as prints on paper, as simpler and easier electronic information, and browsing them have been increasing.
As media displaying such electronic information, recently, an electronic paper has been widely developed as an electronic medium being closer to paper in place of existing displays such as a CRT or a liquid crystal display. For example, an electrochromic display element utilizing coloring and discoloring properties of electrochromic compounds has been widely studied and developed from material development to device designing, since the electrochromic display element is a reflection type display element, exhibits memory characteristics, and can be driven at low voltage. In addition, since the electrochromic display element can develop various colors depending on a structure of the materials, it is also expected to be useful for a multicolor display element.
In recent years, as materials for realizing an electronic device such as those typified by electronic paper, organic-inorganic composite materials have been actively researched. For example, an electrochromic compound has been used, in which the compound is adsorbed on a nano-crystalline layer deposited on an electrode (refer, for example, to Patent Documents 1 and 2).
However, most of the examples have been the developments, as described above, such that a terminal of an acid group of functional organic materials such as a phosphoric acid, a carboxylic acid, and a salicylic acid is adsorbed to hydroxyl groups of inorganic fine particles. Thus, an organic compound can be adsorbed on the inorganic fine particles by employing such acid groups described above, but its bonding force is not so strong that the bonds between the organic compound and the inorganic fine particles are easily broken during fabrication of devices or after repeatedly using the device, or under alkaline conditions to result in problems.
Conventionally, the surface treatment of inorganic fine particles using an organic compound has been widely performed. An example being applied to an electronic device has been disclosed, in which a metal oxide is treated with a silane coupling agent to improve its surface properties (refer, for example, to Patent Document 3), but, the above example simply aimed to improve surface properties of inorganic fine particles. Further, another example of organic-inorganic composite materials was disclosed, in which a metal oxide was treated with a silane coupling agent, and then allowed to react with a functional organic material to produce a bonding between them through a silanol bond (refer, for example, to Patent Document 4). However, the above example had problems such as exhibiting no memory characteristics, low efficiency of the reaction between the functional organic material and the metal oxide so that the control of the amount of the reaction being difficult, and low production adaptability due to complicated production steps of an electrode.
The inventors carried out a diligent examination, and as a result, the inventors found that the above problems can be resolved by introducing a functional silane (a hydrolysable group such as an alkoxysilane or halosilane) as a substituent into an electrochromic compound exhibiting a specific structure.
Patent Document 1: Japanese Translation of PCT International Application Publication No. 2000-506629
Patent Document 2: Unexamined Japanese Patent Application Publication No. (hereinafter, referred to as JP-A) 2007-304164
Patent Document 3: JP-A 2004-191418
Patent Document 4: JP-A 2007-31708